Preparation of a stable cellulose nitrate having good adhesive characteristics



Patented July 22, 1952 PREPARATION OF A STABLE c'E'LLULosn NITRATE HAVING GOOD AnnssIvEoHA ACTERISTICS Donald J. Kridel and William J, eoga' g'imnester, N. Y.,,assignrs to Eastman Kodak Gompany, Rochester,

Jersey,

No Drawing.

This invention relates to the imparting of adhesive characteristics to cellulose nitrate by acting thereon with a solution of H2SO'4 in an inert diluent.

Cellulose nitrate ordinarily is prepared by reacting on cellulose with a mixture of nitric and sulfuric acids, followed by centrifuging and washing with hot water to remove the acids,

therefrom, as described, for example, in U. S. Patent No. 2,118,275 of Talbot. The resulting nitrated cellulose is, however, characterized by mediocre adhesive characteristics in many applications.

One object of our invention is to provide a method of treating cellulose nitrates to improve their adhesive characteristics; Another object of our invention is to prepare stable sulfate containing cellulose nitrates. Other objects will appear herein.

We have found that cellulose nitrates such as in a diluent, acquire adhesive characteristics making'those products useful in any situation where good adhesiveness is desirable. We have found that the treatment of cellulose nitrate with H2804 in a diluent results in imparting thereto a sulfate content within the range of 0.3%-3% which is obtained in accordance with our process in a stable condition. I

.Our invention involves treating cellulose nitrate such as that having a nitrogen contentof -12% nitrogen and a viscosity (A. S. T. M.) of 2-80 seconds with sulfuric acid in a, diluent which doe notgelatinize the nitrocellulose or cause it to lose its structure.

We have found that sulfuric acid concentrations within the range of 10-30% have been the most suitable in preparing products in accordance with our invention. If a proportion of sulfuric acid much higher than 30% is employed; the product which is obtained thereby maybe of such a nature that stabilization thereof would 'be difficult. Consequently, too concene trated sulfuric acid solutions are tobe avoided- On the other hand, with concentrations of sulfuric acid much below 10% the adhesive properties which are imparted to the cellulose nitrate are too slight to warrant the treating of the, cellulose nitrate therewith.-

The diluents employed in our processes should be miscible with sulfuric acid and, yet, should be sufficiently non-solvent of the cellulose nitrate or the product obtained that its fibrous nature is not deteriorated or destroyed. We have N. ,Y.,. a corporation of New Application November 23, 1949, Serial No.129,176

,sola msg (c1. 260-223) found that an liquid acteristics may be employed, water having been found to be particularly good for use as a diluent in our process. We have found, however, that a mixture of aliphatic alcohol of at least four car- 'bon atoms, which is miscible with sulfuric acid,

with a petroleum distillate or some other inert liquid miscible therewith may be employed in such proportion that its miscibility with sulfuric acid is not affected. The petroleum distillate or other inert organic liquid is preferably em ployed in an amount in excess of its miscibility with the alcohol such as 10 30% more, as a matter of economy. If the treating bath is allowed to stand it will, has a result, separate into. two layers. The petroleum. distillates which have been found to be useful mixed with the aliphatic alcohols for this purpose are those having a boilin point within the range of -125 C. Instead of petroleum distillates other liquid hydrocarbons such as toluene, for example, may be employed in this connection. The criterion as to the value of the liquid mixture is its miscibility with sulfuric acid and its inertness to the fibrous structure of the cellulose material. An liquid having these characteristics may be employed as a diluent in preparing cellulose esters having good adhesive characteristics as described herein.

After the reaction of the cellulose nitrate with the sulfuric acid it is desirable to subject it to a further treatment to render the product more stable. This can be accomplished by soaking the product in a dilute solution of an alkali metal hydroxide or an alkali metal salt of a weak acid.

"Some of the stabilizing alkalies which may be employed for this purpose are sodium hydroxide, sodium carbonate, sodium acetate, sodium borate, trisodium phosphate sodium oxalate, or the like. The diluted alkali which is employed to treat the product should be of a strength of at least 0.0 but insufficient to discolor the cellulose 7 form of its solution in alcohol, it should not be employed in a concentration much more than 0.05% toavoid formation of color. If an aqueous solution of .NaOI-I is used-for stabilizing any con centration'up to 0.5%. may be employed without discoloration of the product or causing any substantial viscosity reduction. With sodium acetate, on the other hand, a concentration of which exhibits these charproduct which 1% [thereof may be employed for the stabilizing procedure, while with sodium carbonate and sodium borate concentrations of approximately .4% may be employed. The concentrations given for the solutions of'the various alkalies for stabilizing the cellulose derivative are fairly close to the permissible maximum and the alkali strength used should be near those given. If desired, lesser concentrations of alkali may be em-- ployed and a stabilizing effect will be "obtained 7 governed by the alkali strength and concentration which is used, The most favorable concentration of the alkaline materialig that which is just short of the value which will causediscolora tion of the-product.

I In the treatment of the cellulose nitrate'with sulfuric acid the time of treatment will vary depending uponthe conditions employed. For instance, with diluents which have a softening effect on the cellulose nitrate such as butyl alcohol-hydrocarbon the treatment will take place in less than an hour. On the other hand, if a diluent such as Water is employed, it may even be an advantage to first soften the starting material such as by means of soaking in a pre- 4 V V. nitrocellulose being figured in the parts of reactants present. The following quantities were used:

A3 parts of nitrocellulose (dry weight)- 1015 partsfof 95% sulfuric acid 1969 parts of n-butyl alcohol 3680 parts of Stoddard solvent The liquids after mixing together were brought to atemperature of 75 F. and the dehydrated nitrocellulose was introduced. Moderate stirring was employed and the nitrocellulose was allowed to remain in the fmixture for thirty minutes. The masswas-then centrifuged and washed with butyl alcoholQandthe material was then placed in a butyl alcohol solution containing 0.05% so dium hydroxide for thirty minutes at 75 following which it'was again washed with butyl altreating reagent such as 3% sodium hydroxide for a time. Also, the 'diluent' employed in the stabilizing treatment may be a factor in variation of the time thereof which is employed from one case to the next. This treatment may varyfrom the product in alkali metal hydroxide fora few minutes up to the use of the alkali metal salt of aweak acid for a much longer time.

Th-e jfollowing examples illustrate our inven- {Emmple Z .A dry nitrocellulose having anitrogen content of 11% and an A. S. T; M. solution viscosity of 40 seconds was soaked over night in a .3 solution of sodiumhydroxide. The mass was then washed and was placed in a bath consisting of a 20% aqueous solution of sulfuric acid, the mass having the following composition:

450 parts of nitrocellulose (dry weight) 20 0 parts of E2804 (95%) 798 parts of tap-water and 2 parts of nitricacid'the nitric acid having been added to inhibit corrosion of equipment.

The starting nitrocellulosewas used water wet,

the w aterjcontent having been taken into account in computing the required amounts of sulfuric acid and water for the treatment. The mass was heated to a temperature of 120 F. and was allowed toremain for two hours whereupon fit was cooled to 70 F. and: theacidwas centrifuged therefrom. The product wasavashed with cold tap water'and was thenplacedin a 1% aqueous solution of sodium acetate' for one hour. iThe was; olqtained had thefcllowing analysis: 7 r r I Nitrogen 10.81%

Solution viscosity 21 see. A. S. T. lid.

Sulfate content 1.06%

minutes litmus German heat stability 28 color change Example 2.-Nitroc ellulose having a nitrogen.

content o f'11% and an A. S. T. M. solution viscosity of 16 seconds was reacted upon in a bath prepared by mixing 9 5% sulfuric acid with N- butyl alcohol, this mixing being done by slowly adding thesulfuric'acid to the butyl alcohol with strong agitation and external cooling. The nitrocelluoseemployed was dehydrated and used in that condition, the butyl alcohol contained in the 'cohol. .Ih'e product. of this treatment had the following analysis:

Nitrogen 10.98% Solution viscosity q r 14.5 see. A. S. T. M. Sulfate content 1.00% German heat stability 28 minutes litmus 1 color change The products prepared in accordance with our invention may be employed wherever adhesiveness is wanted. For instance, when dissolved in an organic solvent such as acetone or ethyl alcohol, they are useful as a film cement in the editing of photographic films. The products in accordance with our invention are adapted for use'in situations in which the adherence of one layer to another is not satisfactory. By applying'to one of these layers a thin coating of the product as described herein before applying the second layer ordinarily good adhesivenes's is obtained as the cellulose'derivatives prepared in accordance with our invention are of Wide application in situations of this type. As these products are soluble in methyl or ethyl alcohol, acetone, or othercominonly used organic solvents, they are readily adaptable to coating on. the surface of various types of film base or other sheeting.

We claim:

1. A method of preparing 'a stable cellulosenitrate having good adhesive characteristics which comprises heating cellulose" nitrate having 7 a'10-12% nitrogen content 'and'2450 seconds viscosity with a 10-30% solution of sulfuric acid in a diluent until 0.3 3% sulfate content is imparted thereto, removing the liquid from the V cellulose nitrate and then'soaking itin"a-solu tion of at least 01% concentrationof an alkaline material, selected from the group consisting of the alkali metal hydroxides and the alkali'metal salts of weak acids for a time sufiicient to impart good stability to the cellulose ester.

'2. A method of preparing a stable cellulose nitrate having good adhesive characteristics which comprises heating cellulose nitrate having a 10-12%-nitrcgen content and a viscosity of 2-80 seconds with a 10-30% solution of sulfuric acid in water until a OAS-3% sulfate content is imparted thereto, removing the liquid from the cellulose nitrate and then soaking it in a-solu-. tion of at least .01% concentration of an alkaline material, selected from'the group consisting of the alkali metal hydroxides and the alkali metal salts or weak acids for atime sufficient to impart good stability to the cellulose ester.

A fmethod' 'of preparing a stable cellulose nitrate having good; adhesive characteristics Which comprises heating cellulose nitrate having a -12% nitrogen content and a viscosity of 2-80 seconds with a 10-30% solution of sulfuric acid in an inert diluent consisting of a mixture of a liquid aliphatic alcohol of at least 4 carbon atoms and a liquid hydrocarbon until 03-13% sulfate content is imparted to the cellulose nitrate, removing the liquid therefrom and then soaking the cellulose nitrate in a solution of at least 01% concentration of an alkaline material selected from the group consisting of the alkali metal hydroxides and the alkali metal salts of weak acids for a time suflicient toimpart good stability to the cellulose ester.

4. A method of preparing a stable cellulose nitrate having good adhesive characteristics which comprises heating cellulose nitrate having a 10-12% nitrogen content and ,a viscosity of 2-80 seconds with a v10--30% solution of sulfuric acid in an inert diluent consisting. of butyl alcohol and a petroleum distillate, boiling within the range of 80-125" 0. until 0.3-3% sulfate content is imparted to the cellulose nitrate, removing the liquid therefrom and then soaking the cellulose nitrate in a solution of at least .01% concentration of an alkaline material selected from the alkali metal hydroxides and the alkali metal salts of weak acids for a time sufficient to impart good stability to the cellulose ester.

5. A method of preparing a stable cellulose nitrate having good adhesive characteristics which comprises heating cellulose nitrate having a 10-12% nitrogen content and a viscosity of 2-80 seconds with a 20% aqueous solution of sulfuric acid until a 0.3-3% sulfate content is imparted to the cellulose nitrate, removing the liquid therefrom and then soaking the cellulose nitrate in a solution of approximately 1% of sodium ace- 6 tate for a time suflicient to impart good stability to the cellulose ester.

6. A method of preparing a stable cellulose nitrate having good adhesive characteristics which comprises heating cellulose nitrate having a 10-12%: nitrogen content and a viscosity of 2-80 seconds with a 20% aqueous solution of sulfuric acid until 0.3-3% sulfate content is imparted to the cellulose nitrate, removing the liquid therefrom and then soaking the cellulose nitrate in a solution of sodium hydroxide of approximately 0.05% concentration for a time suificient to impart goodstability to the cellulose ester.

DONALD J. KRIDEL. WILLIAM J. ROGERS.

REFERENCES CITED The following references are of record in the 

1. A MEHOD OF PREPARING A STABLE CELLULOSE NITRATE HAVING GOOD ADHESIVE CHARACTERISTICS WHICH COMPRISES HEATING CELLULOSE NITRATE HAVING A 10-12% NITROGEN CONTENT AND 2-80 SECONDS VISCOSITY WITH A 10-30% SOLUTION OF SULFURIC ACID IN A DILUENT UNTIL 0.3-3% SULFATE CONTENT IS IMPARTED THERETO, REMOVING THE LIQUID FROM THE CELULOSE NITRATE AND THEN SOAKING IT IN A SOLUTION OF AT LEAST .01% CONCENTRATION OF AN ALKALINE MATERIAL, SELECTED FROM THE GROUP CONSISTING OF THE ALKALI METAL HYDROXIDES AND THE ALKALI METAL SALST OF WEAKS ACIDS FOR A TIME SUFFICIENT TO IMPART GOOD STABILITY TO THE CELLULOSE ESTER. 